The present invention relates to a device for applying a composite liquid to a continuously moving web having the form of a belt-like carrier and which is used to manufacture a photographic film, photographic printing paper, a magnetic recording material such as a magnetic recording tape, an adhesive tape, information recording paper such as pressure-sensitive paper and thermosensitive paper, photographic printing plate, or the like. Particularly, the invention relates to a curtain application device employing a slide hopper.
A curtain application device employing a hopper is often used for applying a liquid to a moving web. In such a device, a freely falling curtain of a thin film of one or more kinds of liquid is made to collide against the web so that an applied liquid film is formed on the web. Curtain application devices have long been used for application to furniture, iron plating, etc.
Recently, however, curtain application devices have begun to be used in accuracy-requiring processes such as the manufacture of photographic photosensitive materials, as disclosed in the U.S. Pat. Nos. 3,508,947 and 3,632,374. It is very important for such a curtain application device to uniformly apply a freely falling curtain of a liquid to a moving web at the start of the liquid applying operation of the device. Since the speed of application by the curtain application device is required to be higher than that of an application device employing a slide hopper, the flow rate of the liquid must be made higher in the curtain application device than in the latter. For this reason, it has generally been considered that it is more difficult for a curtain application device to uniformly apply a liquid to a moving web at the start of the liquid applying operation than for a slide-hopper type device. If the liquid is not uniformly applied to the moving web at the start of the operation, problems such as contamination due to spattering of the applied liquid, contamination of a roller due to non-drying of greater thickness portions of the applied liquid downstream to a drying zone can occur, making the final product unacceptable. In the curtain application device disclosed in the U.S. Pat. No. 3,632,374, an application start plate, which is a turnable or slidable deflector, is provided which feeds a prescribed quantity of a liquid at the start of the application of the liquid to form a stable thin curtain. The excess liquid may be recovered and reused.
FIG. 10 shows a side view of the curtain application device disclosed in the U.S. Pat. No. 3,632,374. In this device, liquid 13 flows out from the interior of a slide hopper 11 to a slide surface 12 thereof, and then freely falls in the form of a thin film from the downstream end 14 of the downstream end 14 of the slide surface to form thin curtain 15, which collides against a moving web 16 so as to be applied thereto. Before the curtain 15 begins to be applied to the web 16, the application start plate 18, which is a rectangular flat plate, is in such a position as to prevent the curtain from reaching the web. The liquid first flows down onto the application start plate 18 and is gathered into a recovery vessel 21. The application start plate 18 is then turned about a fulcrum 19 so that the liquid curtain is allowed to reach the web 16, thus starting the application of the liquid curtain to the web.
Both side edges of the curtain 15 are defined by edge guides 20 extending down from the downstream end 14 of the slide hopper 11 to points which are lower than the place where the curtain reaches the web 16.
Although this application device has the advantage that the curtain 15 falling from the slide hopper 11 before the start of the application of the curtain to the web 16 is received by the application start plate 18 and then recovered by the recovery vessel 21 so as to be used again, the device has a first problem in that a large space for turning or sliding the application start plate needs to be provided in the device, a second problem in that the side edge portions of the curtain are always discarded and not applied to the web but have to be recovered for reuse, and a third problem in that, at the instant the application start plate is separated from the curtain at the start of the application thereof, the curtain is applied to the web over the entire width thereof at the same time, making the thickness of the initially applied portion of the liquid on the web larger than in other portions.
The large space, which causes the first problem, needs to be provided so as to make it possible to dispose the slide hopper 11 over the path of the moving web 16 and to make the height of the curtain 15 sufficient. If the liquid is such that the height of the curtain 15 cannot be as high as desired and it can only be made significantly less than that of the slide hopper, the hopper cannot be located over the path of the web and must be located opposite the path across the edge guides 20, making it difficult to turn the application start plate 18 as mentioned above.
The second problem is caused by the fact that the width of the application start plate 18 and the web 16 must be smaller than the distance between the two edge guides 20 so as to be able to turn the plate. If the liquid is made of a single constituent and can therefore be recovered for reuse, or if the liquid is made of plural but less expensive constituents, the application device can be economically operated If, on the other hand, the liquid is made of a large number of constituents and therefore cannot be recovered or the liquid is more expensive, the width of the curtain 15 must be decreased. In that case, the distance between the two edge guides 20 is made smaller than the width of the web 16 or a backup roller 17 so as to place the lower ends of the edge guides in positions which are higher than the line where the curtain 15 collides against the web. If the distance between the web 16 and the edge guides 20 is much increased, the width of the stream of the curtain is decreased, making the applied curtain on the web nonuniform. In that case, the application device, whose application start plate 18 is placed between the web and the guides, cannot be used for the desired applications.
The third problem is caused by liquid accumulation over the point of collision of the curtain 15 against the application start plate 18 receiving the falling curtain before the start of the application to the web 16, which tends to transfer s from the plate 18 to the web 16 at the start of application to the web 16. (See FIG. 11.)